The present invention relates generally to a method for reconstructing the original information (i.e., sound recordings) encoded upon a phonograph record despite wear or damage to the record. The invention recognizes that most or all of the original information may be retrievable, despite the inability of a typical stylus to properly track a worn or damaged groove of the record. The invention has potential application in the fields of sound recording and record reconstruction.
In the sound recording industry, there is substantial interest in restoring old recordings of vocal performances as well as instrumental and orchestral recordings.
One approach to improving the acoustic quality of old sound recordings, as described in U.S. Pat. No. 4,186,280, involves selective amplification or filtration of the acoustic signal mixture, in accordance with the frequency ranges corresponding to the identified sound sources or parts (solo voices, solo instrument, predominant instrumental group and the like) on the record. But suppression or amplification of certain frequencies does not accurately reproduce the original sound.
The motion of a cutting tool 10 in a plastic media encodes sound on phonograph records, as shown in FIG. 1. In mono recordings the cutting tool 10 is moved back and forth in one direction. For stereo recordings, the cutting tool is moved in two orthogonal directions, encoding two channels of stereo signal in the velocity of two orthogonal groove walls (6 and 8 as shown in FIG. 1). The two walls (6 and 8) form a xe2x80x9cVxe2x80x9d groove in the record with each wall forming an angle of approximately 45 degrees with the plane of the record. After a master is cut, multiple copies are made using industry standard pressing techniques.
Standard techniques for playback of records involve measuring the rate of change of the groove position (its xe2x80x9cvelocityxe2x80x9d), typically by a stylus 4 (shown in FIG. 2) which rides in the groove 2 of the record (either the copy or the original cut master). When a record is damaged due to wear, dirt or mishandling, a groove wall 8 may be damaged (exemplified by FIG. 2) so that the playback stylus 4 cannot move in the same manner as was originally encoded on the record. In any system, velocity measurements are quite noisy when small position errors are introduced. In other words, small positional deviations (caused by imperfections or damage) result in large instantaneous velocities. This is a reason why a record degrades so noticeably when it is worn. Small imperfections in the groove are amplified in the velocity signal produced by the stylus. These small positional defects cause sound degradation and often xe2x80x9cclicksxe2x80x9d or xe2x80x9cpopsxe2x80x9d.
Conventionally, record companies attempting to reconstruct old recordings will play a record using different size styli in an effort to read different parts of the groove and interleave the different xe2x80x9cplaysxe2x80x9d of the record. By choosing different size styli, the groove is being tracked at different heights. The goal is to find a location in the groove that is relatively pristine. However, this method has drawbacks because the damage to the groove is often excessive and varies significantly at different locations.
Thus, there continues to be a need to reconstruct sound recordings from a worn or damaged record by means of a method which is true to the originally intended sound recording, whereby damage throughout the record does not create significant unintended noise.
The invention disclosed herein is a method for reconstructing an original groove configuration of a phonograph record. The steps of the method include providing an instrument for making a measurement of an entire groove of a phonograph record, wherein the instrument is in communication with a computer executing reconstructive analysis code. Then the instrument is used to make a measurement of a groove of the phonograph record, and communicating the measurement to the computer and executing the reconstructive analysis code, thereby reconstructing the original groove configuration.
In one embodiment the groove geometry is determined by taking measurements of one or more undamaged portions of the record (the computer may piece these together). Next, the measurements may comprise incremental cross sectional measurements of the groove, which are analyzed by the computer to reconstruct an original cutting tool path, based on the expected groove geometry determined on the first step.
The measurements may be made optically or mechanically. Mechanical measuring instruments may also employ air (fluid) bearing styli, and could comprise a Coordinate Measuring Machine (CMM), scanning electron microscope, a stylus and interferometer apparatus, and/or multiple-probe instruments. An embodiment could also include a flexible stylus for measuring an entire groove cross section simultaneously. Measuring the record at a rate slower than conventional playback allows for use of an instrument with a narrower dynamic range than conventional styli.
In another embodiment, the invention could additionally be used in real time audio playback based upon the reconstructed original record groove configuration.